OFFSET
1,1
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
Will Nicholes, Prime Signatures
MATHEMATICA
f[n_]:=Sort[Last/@FactorInteger[n]]=={1, 9}; Select[Range[90000], f]
PROG
(PARI) list(lim)=my(v=List(), t); forprime(p=2, (lim\2)^(1/9), t=p^9; forprime(q=2, lim\t, if(p==q, next); listput(v, t*q))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 24 2011
(Python)
from sympy import primepi, integer_nthroot, primerange
def A179692(n):
def bisection(f, kmin=0, kmax=1):
while f(kmax) > kmax: kmax <<= 1
kmin = kmax >> 1
while kmax-kmin > 1:
kmid = kmax+kmin>>1
if f(kmid) <= kmid:
kmax = kmid
else:
kmin = kmid
return kmax
def f(x): return n+x-sum(primepi(x//p**9) for p in primerange(integer_nthroot(x, 9)[0]+1))+primepi(integer_nthroot(x, 10)[0])
return bisection(f, n, n) # Chai Wah Wu, Feb 21 2025
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
Vladimir Joseph Stephan Orlovsky, Jul 24 2010
STATUS
approved